This invention relates to aluminizing electroplating cells, which may contain racks for articles, operated with aprotic, oxygen-free and water-free organo-alumino electrolytes in general and more particularly to an electrically insulating protective device for such cells.
It is known that in electroplating facilties when the electroplating voltage is applied between the cathode and the anode, the electrolyte tank must be electrically insulated because of the current conducting property of the electrolytes and the prevailing electric field, because otherwise the electrolyte, as well as the electroplating tank, can suffer damage due to the stray-imparting conduction effect of the electroplating tank if an electrolyte tank of metal is used.
In the customary electroplating technology using an aqueous electrolyte system, the electroplating tanks are therefore made of a suitable plastic material, or if metal is used, the inside surface is rubber coated.
However, this possibility of insulating the electrolyte tank is not applicable from aluminizing electroplating cells operated with aprotic, oxygen-free and water-free organo-aluminum electrolytes. Electrolyte tanks insulated in this manner are also not suited for electroplating facilities such as are described in U.S. Pat. Nos. 4,053,383 and 4,176,934. These organic electrolyte solutions, which are used at about 100.degree. C., over the long term destroy the plastic tanks, or metal tanks with plastic lining, which are customary in electroplating.
In the two aforementioned patents, for example, in FIG. 2 of U.S. Pat. No. 4,053,383, an annular treatment tank is illustrated. Thus, the annular tank includes an inner wall and an outer wall. Adjacent the inner and outer walls and are inner and outer anode segments which form the anode for electroplating. The workpiece holder is disposed between the two anodes and the workpiece forms the cathode.
The electric insulation of the electrolyte tank with respect to an aprotic medium could be solved by providing the inside wall of the tank with an enamel coating (see U.S. Pat. No. 4,053,383). Since enamel is an inorganic material, it is completely resistant. The enamelling process, however, has the disadvantage that larger electrolyte tanks with a volume of several thousand liters can no longer be coated, or coated only at a major expense.
It is an object of the present invention to make metallic electrolyte tanks, especially with large dimensions, more suitable for the electrodeposition of aluminum from aprotic, oxygen-free and water-free organo-aluminum electrolyte systems. The objective is to solve the problem of electric insulation with respect to an aprotic electrolyte system where a metallic electrolyte tank is used.